1. Field of the Invention
The present invention is directed to a method for controlling a pest comprising bringing into contact with the pest a pest-controlling amount of a compound from the group comprising derivatives of xanthine.
2. Description of the Background Art
Despite the recent development and great promise of such . advanced pest-controlling compositions as chemical sterilants, pheromones or ecologically-based insect control strategies, it is doubtless that, at present, the use of chemical pesticides still plays a predominant role. The use of insecticides often represents the difference between profitable crop production for farmers and no marketable crop at all, and the value of insecticides in controlling human and animal diseases has been dramatic.
Therefore, in parallel to the aforementioned newer technologies for pest control, there has been active research and investigation into the detailed biochemical modes of action of existing known chemical pesticides. Thus, for example, Nathanson, et al., Molecular Pharmacology, 20: 68-75 (1981), presented evidence indicating that the formamidine pesticides chlordimeform (CDM) and N-demethylchlordimeform (DCDM) may affect octopaminergic neurotransmission. CDM and DCDM have been reported to mimic the effects of octopamine in stimulating light emission in the firefly lantern (Hollingworth, R. M., et al., Science, 208: 74-76 (1982)) and in effecting nerve-evoked muscle responses in the locust leg (Evans, P. D., Nature, 287: 60-62 (1980)). Nathanson, et al., supra, found that DCDM, which is the probable in vivo metabolite of CDM is about six-fold more potent than octopamine itself as a partial agonist of light organ octopamine-stimulated adenylate cyclase. Stimulation by the formamidines resulted in increased formation of the intracellular messenger, cyclic AMP (cAMP). This stimulation was blocked by cyproheptadine, clozapine, fluphenazine and phentolamine compounds, also known to block the octopamine receptor. Nathanson, et al., concluded that DCDM is the most potent octopaminergic compound described.
Similar results were observed by Hollingworth, et al. (reported in the Scientific Papers of the Institute of Organic and Physical Chemistry of Wroclaw Technical University, No. 22, Conference 7 (1980)). These authors demonstrated that certain formamidines act on octopamine receptors to induce the synthesis of cyclic AMP, and that this response is blocked by both phentolamine and cyproheptadine, which are known to act as octopaminergic antagonists in insects. The authors also suggested that these formamidines are potent stimulators of the octopamine sensitive adenylate cyclases in the thoraxic ganglia of Periplaneta americana, and in the ventral nerve cord and fat body of M. sexta. The authors suggest that the stimulation of octopamine receptors underlies a number of toxic responses seen with formamidines on insects.
It should be noted that the presence of an insect adenylate cyclase enzyme which is sensitive to naturally occurring D(-)octopamine as a "neuro transmitter" has been known for some time (Nathanson, et al., Science 180: 308-310 (1973) (cockroach); Nathanson, Ibid, 203: 65-68 (1979) (firefly); Evans, J., Neurochem., 30: 1015-1022 (1978) (cockroach)).
The study of cyclic AMP as a "second messenger" has led to the accepted model that a hormone or neuro transmitter binds at a cell-membrane bound receptor, which activates adenylate cyclase to a form capable of converting ATP in the cytoplasm of the cell into cAMP. cAMP then relays the signal brought by the hormone or neuro transmitter from the membrane to the interior of the cell. Agonists of the hormone or neuro transmitter are, by definition, capable of eliciting the same response (see, for example, Nathanson and Greengard, Scientific American, 237: 108-119 (1977)). Among other actions, cAMP stimulates the conversion of inactive phosphorylase b into phosphorylase a, a reaction catalysed by phosphorylase kinase. This reaction is, in turn, catalysed by an enzyme, now called protein kinase, which occurs in an inactive and active form. Its active form catalyses the phosphorylation of inactive phosphorylase kinase by ATP to yield the active phosphorylated form by a reaction in which ATP is the phosphate-group donor.
Protein kinase, the key enzyme in linking cAMP to the phosphorylase system and to other cyclic AMP-regulated processes, is an allosteric enzyme, i.e., an enzyme whose reactivity with another molecule is altered by combination with a third molecule that is not a substrate. Its inactive form contains two types of subunits, a catalytic (C) subunit and a regulatory (R) subunit which inhibits the catalytic subunit. cAMP is the allosteric modulator of protein kinase, binding to a specific site on the regulatory subunit and causing the inactive CR complex to dissociate, yielding R-cAMP complex, and the free C subunit, which is now catalytically active. Thus, cAMP removes the inhibition of enzyme activity that is imposed by the binding of the regulatory subunit (Lehninger, Biochemistry, 2nd Ed., pp. 812-813).
The enzyme responsible for the destruction of cAMP is phosphodiesterase, which catalyzes the hydrolytic reaction as follows: ##STR2## It is known that phosphodiesterase activity is inhibited by caffeine and theophylline, alkaloids present in small amounts in coffee and tea. Both caffeine and theophylline have long been known to prolong or intensify the activity of epinephrine, presumably due to increased persistence of cAMP in cells stimulated by epinephrine.
Rojakovick, A. S., et al., Pesticide Biochemistry and Physioloqy, 6:10-19 (1976), explored the interaction between insecticidal activity and cAMP as a secondary messenger, surveying the direct effects of a variety of different types of insecticides upon the activities of adenylate cyclase and phosphodiesterase. The survey of the direct effects of TEPP, methylparaoxon, DDT, Dieldrin, Aldicarb, Dimetilan, Rotenone, Allethrin, and Oxythioquinox upon cockroach brain adenylate cyclase in vitro led the authors to the conclusion that the compounds have essentially no direct effects on adenylate cyclase in vitro. The same nine insecticides were also evaluated for their effect upon cockroach brain phosphodiesterase in vitro. Certain of the compounds showed a general relationship of increasing inhibition with increasing concentration of insecticide, while DDT and Dieldrin appeared to be activators of phosphodiesterase. Oxythioquinox proved to be the most potent inhibitor of cockroach brain phosphodiesterase, giving over 80% inhibition. By comparison, using identical assay techniques, 1,000-fold greater concentrations of aminophylline and theophylline, the most widely used phosphodiesterase inhibitors in adenylate cyclase assays, inhibited 83.2 and 73.8%, respectively. The authors concluded that, while Oxythioquinox and other quinoxoline dithiol derivatives were demonstrated to be potent in vitro inhibitors of phosphodiesterases, no direct relationship of this activity to their mode of toxic action could be determined. Finally, the authors concluded that the broad distribution of phosphodiesterases in the animal kingdom makes it unlikely that phosphodiesterase inhibition is a direct cause of the selective acaricidal activity of the compounds.
Calva, U.S. Pat. No. 2,362,614, describes fluorine-containing insecticides. Disclosed are the hydrofluoric acid addition compounds of ammonia-substituted compounds giving rise to primary, secondary or tertiary amines and polyamines. Insecticidal activity is described as derived from the direct combination of the fluorine-nitrogen link. Caffeine is included in the patent disclosure among the "alkylamines with or without substituent groups."
French Pat. No. 2,138,186 to Aries discloses insecticidal compositions of urinylphosphate esters which are stabilized by purine derivatives. Included among the purine derivatives are purines substituted in the 2, 4 and 8 positions. No insecticidal activity, however, is attributed to the purine compounds, the compounds performing the function of stabilizing the active phosphorus compounds.
Rizvi, S. J. H., et al., Indian J. Exp. Biol., 18: 777-8 (1980), explored the herbicidal activity of ethanolic extracts of leaves and seeds of 49 different plants. The seed extract of Coffea arabica proved most potent. Fractionation of the extract of Coffea arabica in different organic solvents produced a variety of fractions, all of which were tested for the desired activity. The chloroform fraction completely inhibited the seed germination of the test weed at 5,000 ppm. The authors suggested Coffea arabica as a possible source of natural herbicide. The same authors, in Agra. Biol. Chem., 45 (5): 1255-1256 (1981), identified the active weedicidal ingredient as 1,3,7-trimethylxanthine (caffeine). No insecticidal activity for caffeine, however, was disclosed. Rizvi, S. J. H., et al., Journal of Applied Entomoloqy, Vol. 90, No. 4, pp. 378-381 (1980), studied the 1,3,7-tri-methyl-xanthine isolate of Coffea arabica and found it to be effective as a chemosterilant for Callosobrucaus chinensis, causing nearly 100% sterility at a concentration of 1.5%. No suggestion of utility as a pesticidal agent was disclosed.
Given the continuous need for increased selectivity and effectiveness in pest control agents, it became desirable that pesticidal and pestistatic agents from naturally occurring products be developed. Although certain fluorinated amines, including fluorinated caffeine, have been suggested as pesticides (Calva, supra), and although other xanthine derivatives unsubstituted in the 1, 3, and 7 position (the hypoxyxanthines of Aries, supra) have been suggested as stabilizers for phosphate insecticides, and although caffeine has been suggested as a chemisterilant (Rizvi et al., supra), the pesticidal and pestistatic action of substituted xanthine derivatives has not been known prior to this invention.